Typically, when buried metal wiring such as Cu, Damascene, etc., is formed through planarized metal film (such as Cu, W, Al) deposited on a target substrate, such as a semiconductor substrate, CMP (Chemical Mechanical Polishing) can be used.
Also, upon simultaneous formation of the metal buried wirings whose widths may be different from each other, if metal film is deposited on a plurality of grooves whose widths are different, then unevenness (i.e., step differences) may be undesirably formed on the surface of the metal film.
In the past, in an attempt to reduce such unevenness of the metal film, CMP has generally been performed on the target workpiece by controlling the rigidity and rotational speed of a polishing pad used to polish the workpiece.
In the CMP process, a wafer can be rubbed against a rotating polishing pad (or the polishing pad rubbed against the wafer), thereby polishing target surfaces on the wafer, typically so that a variety of films may be polished. The amount of material polished away or removed can depend on the strength or magnitude of the frictional force exerted between the polishing pad and the wafer.
Japanese Patent Publication No.8-155831 entitled, Polishing Apparatus and Polishing Method, proposes to improve the uniformity of the applied frictional force. This patent describes using first and second magnetic field generating bodies for providing magnetic fields. The first magnetic field generating body is generally described as being installed inside of a wafer chuck table and the second magnetic field generating body is described as being configured to generate a repellant magnetic field with respect to the magnetic field generated from the first magnetic field generating body. The second magnetic field generating body is installed in the inside of a turntable, so that an a spacing between the lower side of the wafer chuck table and the upper side of the turntable is maintained parallel to each other due to the repellant force generated by the interaction of the magnetic field generated from the first magnetic field generating body and the magnetic field generated from the second magnetic filed generating body, whereby it is alleged that a more uniform polishing film may be formed.
It is also noted that one of the factors that can determine the strength or intensity of the frictional force applied between the wafer and the polishing pad is the pressure applied to the back of the wafer. U.S. Pat. No. 5,822,243 entitled, Method for Polishing Semiconductor Wafer Using Dynamic Control, proposes an apparatus for controlling the intensity of the pressure applied to the back of the wafer. The content of this patent is hereby incorporated by reference as if recited in full herein. Generally stated, this patent describes a carrier head having a modulation unit. The modulation unit includes a plurality of capacitors having a lower flexibly configured plate and a plurality of upper division plates. A controller monitor can compare capacitance measured between each upper division plate and a lower plate with respect to a predetermined capacitance. If the measured capacitance is different from a predetermined capacitance, the controller monitor can set a voltage operational parameter to a predetermined voltage by controlling an appropriate voltage for each upper division plate. Therefore, the wafer polishing process may be performed dynamically with local adjustability.
In the past, the size of the area where force was applied to the back of the wafer has sometimes been controlled by a pressure change of N2 gas or air. For example, FIG. 1 shows an exemplary configuration of a system used to control pressure by controlling the area over which the force is applied to the back of a wafer 9. As shown in FIG. 1, a rotating turntable 3 includes a polishing pad 1 held on its upper surface. The system also includes a carrier head 10 configured to maintain the spatial alignment or position of the wafer W (shown as object 9) to be polished with respect to the carrier head 10 and/or rotating turntable 3 and polishing pad 1. The system also includes a polishing liquid supplying nozzle 7 for supplying polishing liquid S to the polishing pad 1. As shown in FIG. 1, the carrier head 10 is connected to a shaft 11.
The carrier head 10 has a guide ring 13 of a closed, typically disk, shape that is held at the carrier head's 10 outer peripheral edge so as to trap the object 9 to be polished (the “object” may be referred to for ease of description below as the “wafer”). The guide ring 13 is affixed to the carrier head with its lower surface extending or projecting downward to reside a distance below the lower surface of the carrier head 10. The lower surface of the carrier head 10 can define a maintenance surface. If the wafer 9 detaches from the lower surface of the carrier head 10 during the polishing process, the wafer 9 can be trapped within the guide ring 13 and inside the outer bounds of the carrier head maintenance surface by the guide ring 13 in a first direction (shown as a lateral). At the same time, the wafer 9 is compressed between the carrier head 10 and the polishing pad 1 in a second direction (shown as a longitudinal direction) due to the frictional force applied against the polishing pad 1 during polishing process to inhibit the wafer 9 from moving in the out of operational alignment in the second direction.
As shown in FIG. 2 and FIG. 3, the carrier head 10 can be configured with an air distribution plenum 15 having a plurality of air passages 19a, 19b, 19c extending from an air supply source in fluid communication with the plenum 15 (typically via the shaft 11) to a predetermined respective one of the segment spaces 15a, 15b, 15c. The spaces 15a, 15b, 15c are shown as being in fluid isolation from each other, with lower portions thereof spatially aligned and disposed proximate the lower surface of the carrier head 10. The air passages 19a, 19b, 19c are configured to supply air to a respective predetermined space 15a, 15b, 15c. The air distribution plenum 15 may be configured with the air spaces 15a, 15b, 15c being radially spaced as nested concentric rings defining respective spaces 15a, 15b, 15c, as shown in FIG. 3.
Each divided air distribution plenum space 15a, 15b, 15c has a plurality of air supply members 16a, 16b, 16c that, in operation, direct air into the respective plenum space. The air supply passages 19a, 19b, 19c can comprise tubes that engage the respective air supplying member 16a, 16b, 16c by means of respective connector tubes 17a, 17b, 17c, so that air can be selectively supplied, in serial order, from an air supply source (not shown) to one or more of the air plenum passages 19a, 19b, 19c, to the respective air supply members 16a, 16b, 16c, and then to the respective air plenum space 15a, 15b, 15c. In operation, the air from one or more of the air plenum spaces 15a, 15b, 15c can be released from the lower surface of the carrier head 10 to press the wafer 9. Therefore, the wafer 9 maintains contact force and the polishing process can be performed.
In operation, the polishing apparatus having the foregoing construction can maintain the wafer 9 on the lower surface of the carrier head 10, by applying pressure to the wafer 9 at the polishing pad 1 on the turntable 3 via the carrier head 10. At the same time, the apparatus can polish the wafer 9 by rotating the turntable 3 under the carrier head 10. During operation, as shown in FIG. 2, polishing liquid S is supplied on the polishing pad 1 from the polishing liquid supplying nozzle 7. An example of a conventional polishing liquid is a liquid made of particulates suspended in an alkaline solution. Here, the wafer 9 can be polished by the combined operation of chemical polishing due to the alkaline solution and a mechanical polishing due to the particulates. Unfortunately, the polishing apparatus having the foregoing construction may have problems that contribute to non-uniform polishing. For example, as the air supplying members 16a, 16b, 16c and the air supplying tubes 19a, 19b, 19c are connected via connecting tubes 17a, 17b, 17c, air leaks may be undesirably introduced through the connections potentially applying non-uniform air pressure against the wafer 9. In addition, the air supplying members 16a, 16b, 16c are biased to a local input zone on one side of the concentric plenum spaces 15a, 15b, 15c, each having a relatively small isolated inlet region that directs the air into a larger underlying plenum space. In operation, air supplied via the localized supply inlet members 16a, 16b, 16c is distributed within their corresponding plenum space 15a, 15b, 15c, along arrow directions (orthogonal and/or clockwise and counterclockwise directions, respectively) as shown in FIG. 3. A pressure difference may be generated between the side of the air supplying members 16a, 16b, 16c and a location in the respective plenum substantially opposing the air supplying member location, i.e., such as the portions denoted by A, B, C positioned in the air supply plenum space 15a, 15b, 15c at a location that is substantially opposite to the side holding the respective air supplying member 16a, 16b, 16c. Therefore, the wafer 9 may not be uniformly pressed.